“This is a double cheat, really, on my part because the music also recalled the movie images for me, and on Zep’s part because most of the music and concert footage was rerecorded and reshot much later in a studio. But, hey, the project covered three nights at Madison Square Garden in 1973, when New York was gritty, and there are clips of the city, especially including the subway, and they inspired the feel I wanted for the book.”